Description

This module embeds Lua, via the standard Lua interpreter or LuaJIT, into Nginx and by leveraging Nginx's subrequests, allows the integration of the powerful Lua threads (Lua coroutines) into the Nginx event model.

The Lua interpreter or LuaJIT instance is shared across all the requests in a single nginx worker process but request contexts are segregated using lightweight Lua coroutines.
Loaded Lua modules persist in the nginx worker process level resulting in a small memory footprint even when under heavy loads.

Please note however, that Lua code written inline within nginx.conf
such as those specified by set_by_lua, content_by_lua,
access_by_lua, and rewrite_by_lua will always be
cached because only the Nginx config file parser can correctly parse the nginx.conf
file and the only ways to to reload the config file
are to send a HUP signal or to restart Nginx.

The ngx_lua module does not currently support the stat mode available with the
Apache mod_lua module but this is planned for implementation in the future.

Disabling the Lua code cache is strongly
discouraged for production use and should only be used during
development as it has a significant negative impact on overall performance.
In addition, race conditions when reloading Lua modules are common for concurrent requests
when the code cache is disabled.

lua_regex_cache_max_entries

syntax:lua_regex_cache_max_entries <num>

default:lua_regex_cache_max_entries 1024

context:http

Specifies the maximum number of entries allowed in the worker process level compiled regex cache.

The default number of entries allowed is 1024 and when this limit is reached, new regular expressions will not be cached (as if the o option was not specified) and there will be one, and only one, warning in the error.log file:

Do not activate the o option for regular expressions (and/or replace string arguments for ngx.re.sub and ngx.re.gsub) that are generated on the fly and give rise to infinite variations to avoid hitting the specified limit.

lua_package_path

Sets the Lua module search path used by scripts specified by set_by_lua,
content_by_lua and others. The path string is in standard Lua path form, and ;;
can be used to stand for the original search paths.

As from the v0.5.0rc29 release, the special notation $prefix or ${prefix} can be used in the search path string to indicate the path of the server prefix usually determined by the -p PATH command-line option while starting the Nginx server.

lua_package_cpath

Sets the Lua C-module search path used by scripts specified by set_by_lua,
content_by_lua and others. The cpath string is in standard Lua cpath form, and ;;
can be used to stand for the original cpath.

As from the v0.5.0rc29 release, the special notation $prefix or ${prefix} can be used in the search path string to indicate the path of the server prefix usually determined by the -p PATH command-line option while starting the Nginx server.

init_by_lua

syntax:init_by_lua <lua-script-str>

context:http

phase:loading-config

Runs the Lua code specified by the argument <lua-script-str> on the global Lua VM level when the Nginx master process (if any) is loading the Nginx config file.

When Nginx receives the HUP signal and starts reloading the config file, the Lua VM will also be re-created and init_by_lua will run again on the new Lua VM.

Usually you can register (true) Lua global variables or pre-load Lua modules at server start-up by means of this hook. Here is an example for pre-loading Lua modules:

But note that, the lua_shared_dict's shm storage will not be cleared through a config reload (via the HUP signal, for example). So if you do not want to re-initialize the shm storage in your init_by_lua code in this case, then you just need to set a custom flag in the shm storage and always check the flag in your init_by_lua code.

Because the Lua code in this context runs before Nginx forks its worker processes (if any), data or code loaded here will enjoy the Copy-on-write (COW) feature provided by many operating systems among all the worker processes, thus saving a lot of memory.

More Nginx APIs for Lua may be supported in this context upon future user requests.

Basically you can safely use Lua libraries that do blocking I/O in this very context because blocking the master process during server start-up is completely okay. Even the Nginx core does blocking I/O (at least on resolving upstream's host names) at the configure-loading phase.

You should be very careful about potential security vulnerabilities in your Lua code registered in this context because the Nginx master process is often run under the root account.

When a relative path like foo/bar.lua is given, they will be turned into the absolute path relative to the server prefix path determined by the -p PATH command-line option while starting the Nginx server.

This directive was first introduced in the v0.5.5 release.

set_by_lua

syntax:set_by_lua $res <lua-script-str> [$arg1 $arg2 ...]

context:server, server if, location, location if

phase:server-rewrite, rewrite

Executes code specified in <lua-script-str> with optional input arguments $arg1 $arg2 ..., and returns string output to $res.
The code in <lua-script-str> can make API calls and can retrieve input arguments from the ngx.arg table (index starts from 1 and increases sequentially).

This directive is designed to execute short, fast running code blocks as the Nginx event loop is blocked during code execution. Time consuming code sequences should therefore be avoided.

Note that the following API functions are currently disabled within this context:

set_by_lua_file

Equivalent to set_by_lua, except that the file specified by <path-to-lua-script-file> contains the Lua code, or, as from the v0.5.0rc32 release, the Lua/LuaJIT bytecode to be executed.

Nginx variable interpolation is supported in the <path-to-lua-script-file> argument string of this directive. But special care must be taken for injection attacks.

When a relative path like foo/bar.lua is given, they will be turned into the absolute path relative to the server prefix path determined by the -p PATH command-line option while starting the Nginx server.

When the Lua code cache is turned on (by default), the user code is loaded once at the first request and cached
and the Nginx config must be reloaded each time the Lua source file is modified.
The Lua code cache can be temporarily disabled during development by
switching lua_code_cacheoff in nginx.conf to avoid reloading Nginx.

content_by_lua

syntax:content_by_lua <lua-script-str>

context:location, location if

phase:content

Acts as a "content handler" and executes Lua code string specified in <lua-script-str> for every request.
The Lua code may make API calls and is executed as a new spawned coroutine in an independent global environment (i.e. a sandbox).

Do not use this directive and other content handler directives in the same location. For example, this directive and the proxy_pass directive should not be used in the same location.

content_by_lua_file

syntax:content_by_lua_file <path-to-lua-script-file>

context:location, location if

phase:content

Equivalent to content_by_lua, except that the file specified by <path-to-lua-script-file> contains the Lua code, or, as from the v0.5.0rc32 release, the Lua/LuaJIT bytecode to be executed.

Nginx variables can be used in the <path-to-lua-script-file> string to provide flexibility. This however carries some risks and is not ordinarily recommended.

When a relative path like foo/bar.lua is given, they will be turned into the absolute path relative to the server prefix path determined by the -p PATH command-line option while starting the Nginx server.

When the Lua code cache is turned on (by default), the user code is loaded once at the first request and cached
and the Nginx config must be reloaded each time the Lua source file is modified.
The Lua code cache can be temporarily disabled during development by
switching lua_code_cacheoff in nginx.conf to avoid reloading Nginx.

rewrite_by_lua

syntax:rewrite_by_lua <lua-script-str>

context:http, server, location, location if

phase:rewrite tail

Acts as a rewrite phase handler and executes Lua code string specified in <lua-script-str> for every request.
The Lua code may make API calls and is executed as a new spawned coroutine in an independent global environment (i.e. a sandbox).

Note that this handler always runs after the standard HttpRewriteModule. So the following will work as expected:

Just as any other rewrite phase handlers, rewrite_by_lua also runs in subrequests.

Note that when calling ngx.exit(ngx.OK) within a rewrite_by_lua handler, the nginx request processing control flow will still continue to the content handler. To terminate the current request from within a rewrite_by_lua handler, calling ngx.exit with status >= 200 (ngx.HTTP_OK) and status < 300 (ngx.HTTP_SPECIAL_RESPONSE) for successful quits and ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR) (or its friends) for failures.

Here the Lua code ngx.exit(503) will never run. This will be the case if rewrite ^ /bar last is used as this will similarly initiate an internal redirection. If the break modifier is used instead, there will be no internal redirection and the rewrite_by_lua code will be executed.

The rewrite_by_lua code will always run at the end of the rewrite request-processing phase unless rewrite_by_lua_no_postpone is turned on.

rewrite_by_lua_file

syntax:rewrite_by_lua_file <path-to-lua-script-file>

context:http, server, location, location if

phase:rewrite tail

Equivalent to rewrite_by_lua, except that the file specified by <path-to-lua-script-file> contains the Lua code, or, as from the v0.5.0rc32 release, the Lua/LuaJIT bytecode to be executed.

Nginx variables can be used in the <path-to-lua-script-file> string to provide flexibility. This however carries some risks and is not ordinarily recommended.

When a relative path like foo/bar.lua is given, they will be turned into the absolute path relative to the server prefix path determined by the -p PATH command-line option while starting the Nginx server.

When the Lua code cache is turned on (by default), the user code is loaded once at the first request and cached and the Nginx config must be reloaded each time the Lua source file is modified. The Lua code cache can be temporarily disabled during development by switching lua_code_cacheoff in nginx.conf to avoid reloading Nginx.

The rewrite_by_lua_file code will always run at the end of the rewrite request-processing phase unless rewrite_by_lua_no_postpone is turned on.

access_by_lua

syntax:access_by_lua <lua-script-str>

context:http, server, location, location if

phase:access tail

Acts as an access phase handler and executes Lua code string specified in <lua-script-str> for every request.
The Lua code may make API calls and is executed as a new spawned coroutine in an independent global environment (i.e. a sandbox).

Note that this handler always runs after the standard HttpAccessModule. So the following will work as expected:

As with other access phase handlers, access_by_lua will not run in subrequests.

Note that when calling ngx.exit(ngx.OK) within a access_by_lua handler, the nginx request processing control flow will still continue to the content handler. To terminate the current request from within a access_by_lua handler, calling ngx.exit with status >= 200 (ngx.HTTP_OK) and status < 300 (ngx.HTTP_SPECIAL_RESPONSE) for successful quits and ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR) (or its friends) for failures.

access_by_lua_file

syntax:access_by_lua_file <path-to-lua-script-file>

context:http, server, location, location if

phase:access tail

Equivalent to access_by_lua, except that the file specified by <path-to-lua-script-file> contains the Lua code, or, as from the v0.5.0rc32 release, the Lua/LuaJIT bytecode to be executed.

Nginx variables can be used in the <path-to-lua-script-file> string to provide flexibility. This however carries some risks and is not ordinarily recommended.

When a relative path like foo/bar.lua is given, they will be turned into the absolute path relative to the server prefix path determined by the -p PATH command-line option while starting the Nginx server.

When the Lua code cache is turned on (by default), the user code is loaded once at the first request and cached
and the Nginx config must be reloaded each time the Lua source file is modified.
The Lua code cache can be temporarily disabled during development by switching lua_code_cacheoff in nginx.conf to avoid repeatedly reloading Nginx.

When a relative path like foo/bar.lua is given, they will be turned into the absolute path relative to the server prefix path determined by the -p PATH command-line option while starting the Nginx server.

body_filter_by_lua

The input data chunk is passed via ngx.arg1 and the "eof" flag indicating the end of the response body data stream is passed via ngx.arg2.

Behind the scene, the "eof" flag is just the last_buf flag of the nginx chain link buffers. And in the context of an Nginx subrequest, there is no "eof" flag at all, due to the underlying limitation in the Nginx core.

The output data stream can be aborted immediately by running the following Lua statement:

return ngx.ERROR

This will truncate the response body and usually result in incomplete and also invalid responses.

The Lua code can pass its own modified version of the input data chunk to the downstream Nginx output body filters by overriding ngx.arg[1] with a Lua string or a Lua table of strings. For example, to transform all the lowercase letters in the response body, we can just write:

Nginx output filters may be called multiple times for a single request because response body may be delivered in chunks. Thus, the Lua code specified by in this directive may also run multiple times in the lifetime of a single HTTP request.

This directive was first introduced in the v0.5.0rc32 release.

body_filter_by_lua_file

syntax:body_filter_by_lua_file <path-to-lua-script-file>

context:http, server, location, location if

phase:output-body-filter

Equivalent to body_filter_by_lua, except that the file specified by <path-to-lua-script-file> contains the Lua code, or, as from the v0.5.0rc32 release, the Lua/LuaJIT bytecode to be executed.

When a relative path like foo/bar.lua is given, they will be turned into the absolute path relative to the server prefix path determined by the -p PATH command-line option while starting the Nginx server.

This directive was first introduced in the v0.5.0rc32 release.

log_by_lua

syntax:log_by_lua <lua-script-str>

context:http, server, location, location if

phase:log

Run the Lua source code inlined as the <lua-script-str> at the log request processing phase. This does not replace the current access logs, but runs after.

Note that the following API functions are currently disabled within this context:

log_by_lua_file

Equivalent to log_by_lua, except that the file specified by <path-to-lua-script-file> contains the Lua code, or, as from the v0.5.0rc32 release, the Lua/LuaJIT bytecode to be executed.

When a relative path like foo/bar.lua is given, they will be turned into the absolute path relative to the server prefix path determined by the -p PATH command-line option while starting the Nginx server.

This directive was first introduced in the v0.5.0rc31 release.

lua_need_request_body

syntax:lua_need_request_body <on|off>

default:off

context:main | server | location

phase:depends on usage

Determines whether to force the request body data to be read before running rewrite/access/access_by_lua* or not. The Nginx core does not read the client request body by default and if request body data is required, then this directive should be turned on or the ngx.req.read_body function should be called within the Lua code.

If the current location includes rewrite_by_lua or rewrite_by_lua_file directives,
then the request body will be read just before the rewrite_by_lua or rewrite_by_lua_file code is run (and also at the
rewrite phase). Similarly, if only content_by_lua is specified,
the request body will not be read until the content handler's Lua code is
about to run (i.e., the request body will be read during the content phase).

lua_socket_connect_timeout

This directive controls the default timeout value used in TCP/unix-domain socket object's connect method and can be overridden by the settimeout method.

The <time> argument can be an integer, with an optional time unit, like s (second), ms (millisecond), m (minute). The default time unit is s, i.e., "second". The default setting is 60s.

This directive was first introduced in the v0.5.0rc1 release.

lua_socket_send_timeout

syntax:lua_socket_send_timeout <time>

default:lua_socket_send_timeout 60s

context:http, server, location

Controls the default timeout value used in TCP/unix-domain socket object's send method and can be overridden by the settimeout method.

The <time> argument can be an integer, with an optional time unit, like s (second), ms (millisecond), m (minute). The default time unit is s, i.e., "second". The default setting is 60s.

This directive was first introduced in the v0.5.0rc1 release.

lua_socket_send_lowat

syntax:lua_socket_send_lowat <size>

default:lua_socket_send_lowat 0

context:http, server, location

Controls the lowat (low water) value for the cosocket send buffer.

lua_socket_read_timeout

syntax:lua_socket_read_timeout <time>

default:lua_socket_read_timeout 60s

context:http, server, location

phase:depends on usage

This directive controls the default timeout value used in TCP/unix-domain socket object's receive method and iterator functions returned by the receiveuntil method. This setting can be overridden by the settimeout method.

The <time> argument can be an integer, with an optional time unit, like s (second), ms (millisecond), m (minute). The default time unit is s, i.e., "second". The default setting is 60s.

This directive was first introduced in the v0.5.0rc1 release.

lua_socket_buffer_size

syntax:lua_socket_buffer_size <size>

default:lua_socket_buffer_size 4k/8k

context:http, server, location

Specifies the buffer size used by cosocket reading operations.

This buffer does not have to be that big to hold everything at the same time because cosocket supports 100% non-buffered reading and parsing. So even 1 byte buffer size should still work everywhere but the performance could be terrible.

This directive was first introduced in the v0.5.0rc1 release.

lua_socket_pool_size

syntax:lua_socket_pool_size <size>

default:lua_socket_pool_size 30

context:http, server, location

Specifies the size limit (in terms of connection count) for every cosocket connection pool associated with every remote server (i.e., identified by either the host-port pair or the unix domain socket file path).

Default to 30 connections for every pool.

When the connection pool is exceeding the size limit, the least recently used (idle) connection already in the pool will be closed automatically to make room for the current connection.

Note that the cosocket connection pool is per nginx worker process rather than per nginx server instance, so so size limit specified here also applies to every single nginx worker process.

This directive was first introduced in the v0.5.0rc1 release.

lua_socket_keepalive_timeout

syntax:lua_socket_keepalive_timeout <time>

default:lua_socket_keepalive_timeout 60s

context:http, server, location

This directive controls the default maximal idle time of the connections in the cosocket built-in connection pool. When this timeout reaches, idle connections will be closed automatically and removed from the pool. This setting can be overridden by cosocket objects' setkeepalive method.

The <time> argument can be an integer, with an optional time unit, like s (second), ms (millisecond), m (minute). The default time unit is s, i.e., "second". The default setting is 60s.

This directive was first introduced in the v0.5.0rc1 release.

lua_http10_buffering

syntax:lua_http10_buffering on|off

default:lua_http10_buffering on

context:http, server, location, location-if

Enables or disables the automatic response caching for HTTP 1.0 (or older) requests. This buffering mechanism is mainly used for HTTP 1.0 keep-alive which replies on a proper Content-Length response header.

If the Lua code explicitly sets a Content-Length response header before sending the headers (either explicitly via ngx.send_headers or implicitly via the first ngx.say or ngx.print call).

To output very large response data in a streaming fashion (via the ngx.flush call, for example), this directive MUST be turned off to minimize memory usage.

This directive is turned on by default.

This directive was first introduced in the v0.5.0rc19 release.

rewrite_by_lua_no_postpone

syntax:rewrite_by_lua_no_postpone on|off

default:rewrite_by_lua_no_postpone off

context:http, server, location, location-if

Controls whether or not to disable postponing rewrite_by_lua and rewrite_by_lua_file directives to run at the end of the rewrite request-processing phase. By default, this directive is turned off and the Lua code is postponed to run at the end of the rewrite phase.

This directive was first introduced in the v0.5.0rc29 release.

lua_transform_underscores_in_response_headers

syntax:lua_transform_underscores_in_response_headers on|off

default:lua_transform_underscores_in_response_headers on

context:http, server, location, location-if

Controls whether to transform underscores (_) in the response header names specified in the ngx.header.HEADER API to hypens (-).

This directive was first introduced in the v0.5.0rc32 release.

Nginx API for Lua

Introduction

The various *_by_lua and *_by_lua_file configuration directives serve as gateways to the Lua API within the nginx.conf file. The Nginx Lua API described below can only be called within the user Lua code run in the context of these configuration directives.

The API is exposed to Lua in the form of two standard packages ngx and ndk. These packages are in the default global scope within ngx_lua and are always available within ngx_lua directives.

The packages can be introduced into external Lua modules by using the package.seeall option:

module("my_module", package.seeall)
function say(a) ngx.say(a) end

Alternatively, they can be imported to external Lua modules by using file scoped local Lua variables:

local ngx = ngx
module("my_module")
function say(a) ngx.say(a) end

It is also possible to directly require the packages in external Lua modules:

local ngx = require "ngx"
local ndk = require "ndk"

The ability to require these packages was introduced in the v0.2.1rc19 release.

Network I/O operations in user code should only be done through the Nginx Lua API calls as the Nginx event loop may be blocked and performance drop off dramatically otherwise. Disk operations with relatively small amount of data can be done using the standard Lua io library but huge file reading and writing should be avoided wherever possible as they may block the Nginx process significantly. Delegating all network and disk I/O operations to Nginx's subrequests (via the ngx.location.capture method and similar) is strongly recommended for maximum performance.

ngx.arg

syntax:val = ngx.arg[index]

context:set_by_lua, body_filter_by_lua**

When this is used in the context of the set_by_lua or set_by_lua_file directives, this table is read-only and holds the input arguments to the config directives:

When this table is used in the context of body_filter_by_lua or body_filter_by_lua_file, the first element holds the input data chunk to the output filter code and the second element holds the boolean flag for the "eof" flag indicating the end of the whole output data stream.

The data chunk and "eof" flag passed to the downstream Nginx output filters can also be overridden by assigning values directly to the corresponding table elements. When setting nil or an empty Lua string value to ngx.arg[1], no data chunk will be passed to the downstream Nginx output filters at all.

Note that only three of these constants are utilized by the Nginx API for Lua (i.e., ngx.exit accepts NGX_OK, NGX_ERROR, and NGX_DECLINED as input).

ngx.null

The ngx.null constant is a NULL light userdata usually used to represent nil values in Lua tables etc and is similar to the lua-cjson library's cjson.null constant. This constant was first introduced in the v0.5.0rc5 release.

The ngx.DECLINED constant was first introduced in the v0.5.0rc19 release.

print

Writes argument values into the nginx error.log file with the ngx.NOTICE log level.

It is equivalent to

ngx.log(ngx.NOTICE, ...)

Lua nil arguments are accepted and result in literal "nil" strings while Lua booleans result in literal "true" or "false" strings. And the ngx.null constant will yield the "null" string output.

There is a hard coded 2048 byte limitation on error message lengths in the Nginx core. This limit includes trailing newlines and leading time stamps. If the message size exceeds this limit, Nginx will truncate the message text accordingly. This limit can be manually modified by editing the NGX_MAX_ERROR_STR macro definition in the src/core/ngx_log.h file in the Nginx source tree.

Arbitrary data values, including Lua closures and nested tables, can be inserted into this "magic" table. It also allows the registration of custom meta methods.

Overriding ngx.ctx with a new Lua table is also supported, for example,

ngx.ctx = { foo = 32, bar = 54 }

ngx.location.capture

syntax:res = ngx.location.capture(uri, options?)

context:rewrite_by_lua, access_by_lua, content_by_lua*

Issue a synchronous but still non-blocking Nginx Subrequest using uri.

Nginx's subrequests provide a powerful way to make non-blocking internal requests to other locations configured with disk file directory or any other nginx C modules like ngx_proxy, ngx_fastcgi, ngx_memc,
ngx_postgres, ngx_drizzle, and even ngx_lua itself and etc etc etc.

Also note that subrequests just mimic the HTTP interface but there is no extra HTTP/TCP traffic nor IPC involved. Everything works internally, efficiently, on the C level.

Returns a Lua table with three slots (res.status, res.header, and res.body).

res.header holds all the response headers of the
subrequest and it is a normal Lua table. For multi-value response headers,
the value is a Lua (array) table that holds all the values in the order that
they appear. For instance, if the subrequest response headers contain the following
lines:

Set-Cookie: a=3
Set-Cookie: foo=bar
Set-Cookie: baz=blah

Then res.header["Set-Cookie"] will be evaluated to the table value
{"a=3", "foo=bar", "baz=blah"}.

URI query strings can be concatenated to URI itself, for instance,

res = ngx.location.capture('/foo/bar?a=3&b=4')

Named locations like @foo are not allowed due to a limitation in
the nginx core. Use normal locations combined with the internal directive to
prepare internal-only locations.

An optional option table can be fed as the second
argument, which supports the options:

method
specify the subrequest's request method, which only accepts constants like ngx.HTTP_POST.

ctx
specify a Lua table to be the ngx.ctx table for the subrequest. It can be the current request's ngx.ctx table, which effectively makes the parent and its subrequest to share exactly the same context table. This option was first introduced in the v0.3.1rc25 release.

vars
take a Lua table which holds the values to set the specified Nginx variables in the subrequest as this option's value. This option was first introduced in the v0.3.1rc31 release.

copy_all_vars
specify whether to copy over all the Nginx variable values of the current request to the subrequest in question. modifications of the nginx variables in the subrequest will not affect the current (parent) request. This option was first introduced in the v0.3.1rc31 release.

share_all_vars
specify whether to share all the Nginx variables of the subrequest with the current (parent) request. modifications of the Nginx variables in the subrequest will affect the current (parent) request.

See HTTP method constants methods other than POST.
The method option is ngx.HTTP_GET by default.

The args option can specify extra URI arguments, for instance,

ngx.location.capture('/foo?a=1',
{ args = { b = 3, c = ':' } }
)

is equivalent to

ngx.location.capture('/foo?a=1&b=3&c=%3a')

that is, this method will automatically escape argument keys and values according to URI rules and
concatenating them together into a complete query string. The format for the Lua table passed as the args argument is identical to the format used in the ngx.encode_args method.

The args option can also take plain query strings:

ngx.location.capture('/foo?a=1',
{ args = 'b=3&c=%3a' } }
)

This is functionally identical to the previous examples.

The share_all_vars option controls whether to share nginx variables among the current request and its subrequests.
If this option is set to true, then the current request and associated subrequests will share the same Nginx variable scope. Hence, changes to Nginx variables made by a subrequest will affect the current request.

Care should be taken in using this option as variable scope sharing can have unexpected side effects. The args, vars, or copy_all_vars options are generally preferable instead.

The copy_all_vars option provides a copy of the parent request's Nginx variables to subrequests when such subrequests are issued. Changes made to these variables by such subrequests will not affect the parent request or any other subrequests sharing the parent request's variables.

Note that if both share_all_vars and copy_all_vars are set to true, then share_all_vars takes precedence.

In addition to the two settings above, it is possible to specify
values for variables in the subrequest using the vars option. These
variables are set after the sharing or copying of variables has been
evaluated, and provides a more efficient method of passing specific
values to a subrequest over encoding them as URL arguments and
unescaping them in the Nginx config file.

Note that subrequests issued by ngx.location.capture inherit all the
request headers of the current request by default and that this may have unexpected side effects on the
subrequest responses. For example, when using the standard ngx_proxy module to serve
subrequests, an "Accept-Encoding: gzip" header in the main request may result
in gzipped responses that cannot be handled properly in Lua code. Original request headers should be ignored by setting
proxy_pass_request_headers to off in subrequest locations.

There is a hard-coded upper limit on the number of concurrent subrequests possible for every main request. In older versions of Nginx, the limit was 50 concurrent subrequests and in more recent versions, Nginx 1.1.x onwards, this was increased to 200 concurrent subrequests. When this limit is exceeded, the following error message is added to the error.log file:

[error] 13983#0: *1 subrequests cycle while processing "/uri"

The limit can be manually modified if required by editing the definition of the NGX_HTTP_MAX_SUBREQUESTS macro in the nginx/src/http/ngx_http_request.h file in the Nginx source tree.

ngx.req.set_uri

Rewrite the current request's (parsed) URI by the uri argument. The uri argument must be a Lua string and cannot be of zero length, or a Lua exception will be thrown.

The optional boolean jump argument can trigger location rematch (or location jump) as HttpRewriteModule's rewrite directive, that is, when jump is true (default to false), this function will never return and it will tell Nginx to try re-searching locations with the new URI value at the later post-rewrite phase and jumping to the new location.

Location jump will not be triggered otherwise, and only the current request's URI will be modified, which is also the default behavior. This function will return but with no returned values when the jump argument is false or absent altogether.

Note that a maximum of 100 request arguments are parsed by default (including those with the same name) and that additional request arguments are silently discarded to guard against potential denial of service attacks.

However, the optional max_args function argument can be used to override this limit:

local args = ngx.req.get_uri_args(10)

This argument can be set to zero to remove the limit and to process all request arguments received:

local args = ngx.req.get_uri_args(0)

Removing the max_args cap is strongly discouraged.

ngx.req.get_post_args

Returns a Lua table holding all the current request POST query arguments (of the MIME type application/x-www-form-urlencoded). Call ngx.req.read_body to read the request body first or turn on the lua_need_request_body directive to avoid Lua exception errors.

Note that a maximum of 100 request arguments are parsed by default (including those with the same name) and that additional request arguments are silently discarded to guard against potential denial of service attacks.

However, the optional max_args function argument can be used to override this limit:

local args = ngx.req.get_post_args(10)

This argument can be set to zero to remove the limit and to process all request arguments received:

Note that the ngx.var.HEADER API call, which uses core $http_HEADER variables, may be more preferable for reading individual request headers.

For multiple instances of request headers such as:

Foo: foo
Foo: bar
Foo: baz

the value of ngx.req.get_headers()["Foo"] will be a Lua (array) table such as:

{"foo", "bar", "baz"}

Note that a maximum of 100 request headers are parsed by default (including those with the same name) and that additional request headers are silently discarded to guard against potential denial of service attacks.

However, the optional max_headers function argument can be used to override this limit:

local args = ngx.req.get_headers(10)

This argument can be set to zero to remove the limit and to process all request headers received:

If the request body is already read previously by turning on lua_need_request_body or by using other modules, then this function does not run and returns immediately.

If the request body has already been explicitly discarded, either by the ngx.req.discard_body function or other modules, this function does not run and returns immediately.

In case of errors, such as connection errors while reading the data, this method will throw out a Lua exception or terminate the current request with a 500 status code immediately.

The request body data read using this function can be retrieved later via ngx.req.get_body_data or, alternatively, the temporary file name for the body data cached to disk using ngx.req.get_body_file. This depends on

In cases where current request may have a request body and the request body data is not required, The ngx.req.discard_body function must be used to explicitly discard the request body to avoid breaking things under HTTP 1.1 keepalive or HTTP 1.1 pipelining.

This function was first introduced in the v0.3.1rc17 release.

ngx.req.discard_body

syntax:ngx.req.discard_body()

context:rewrite_by_lua, access_by_lua, content_by_lua*

Explicitly discard the request body, i.e., read the data on the connection and throw it away immediately. Please note that ignoring request body is not the right way to discard it, and that this function must be called to avoid breaking things under HTTP 1.1 keepalive or HTTP 1.1 pipelining.

This function is an asynchronous call and returns immediately.

If the request body has already been read, this function does nothing and returns immediately.

ngx.req.get_body_data

syntax:data = ngx.req.get_body_data()

context:rewrite_by_lua, access_by_lua, content_by_lua*

Retrieves in-memory request body data. It returns a Lua string rather than a Lua table holding all the parsed query arguments. Use the ngx.req.get_post_args function instead if a Lua table is required.

This function returns nil if
1. the request body has not been read,
1. the request body has been read into disk temporary files,
1. or the request body has zero size.

If the request body has not been read yet, call ngx.req.read_body first (or turned on lua_need_request_body to force this module to read the request body automatically, but this is not recommended).

If the request body has been read into disk files, try calling the ngx.req.get_body_file function instead.

ngx.req.set_body_data

syntax:ngx.req.set_body_data(data)

context:rewrite_by_lua, access_by_lua, content_by_lua*

Set the current request's request body using the in-memory data specified by the data argument.

If the current request's request body has not been read, then it will be properly discarded. When the current request's request body has been read into memory or buffered into a disk file, then the old request body's memory will be freed or the disk file will be cleaned up immediately, respectively.

This function requires patching the Nginx core to function properly because the Nginx core does not allow modifying request bodies by the current design. Here is a patch for Nginx 1.0.11: nginx-1.0.11-allow_request_body_updating.patch, and this patch should be applied cleanly to other releases of Nginx as well.

This patch has already been applied to ngx_openresty 1.0.8.17 and above.

ngx.req.set_body_file

Set the current request's request body using the in-file data specified by the file_name argument.

If the optional auto_clean argument is given a true value, then this file will be automatically removed at request completion or the next time this function or ngx.req.set_body_data are called in the same request. The auto_clean is default to false.

Please ensure that the file specified by the file_name argument exists and is readable by an Nginx worker process by setting its permission properly to avoid Lua exception errors.

If the current request's request body has not been read, then it will be properly discarded. When the current request's request body has been read into memory or buffered into a disk file, then the old request body's memory will be freed or the disk file will be cleaned up immediately, respectively.

This function requires patching the Nginx core to function properly because the Nginx core does not allow modifying request bodies by the current design. Here is a patch for Nginx 1.0.9: nginx-1.0.9-allow_request_body_updating.patch, and this patch should be applied cleanly to other releases of Nginx as well.
This patch has already been applied to ngx_openresty 1.0.8.17 and above.

If the buffer_size argument is specified, then its value will be used for the size of the memory buffer for body writing with ngx.req.append_body. If the argument is omitted, then the value specified by the standard client_body_buffer_size directive will be used instead.

When the data can no longer be hold in the memory buffer for the request body, then the data will automatically be flushed onto a temporary file just like the standard request body reader in the Nginx core.

It is important to always call the ngx.req.finish_body after all the data has been appended onto the current request body. Also, when this function is used together with ngx.req.socket, it is required to call ngx.req.socketbefore this function, or you will get the "request body already exists" error message.

The usage of this function is often like this:

ngx.req.init_body(128 * 1024) -- buffer is 128KB
for chunk in next_data_chunk() do
ngx.req.append_body(chunk) -- each chunk can be 4KB
end
ngx.req.finish_body()

ngx.req.append_body

Append new data chunk specified by the data_chunk argument onto the existing request body created by the ngx.req.init_body call.

When the data can no longer be hold in the memory buffer for the request body, then the data will automatically be flushed onto a temporary file just like the standard request body reader in the Nginx core.

It is important to always call the ngx.req.finish_body after all the data has been appended onto the current request body.

If there is any request body data that has been pre-read into the Nginx core's request header buffer, the resulting cosocket object will take care of that automatically. So there will not be any data loss due to potential body data pre-reading.

This method is very much like the rewrite directive with the redirect modifier in the standard
HttpRewriteModule, for example, this nginx.conf snippet

rewrite ^ /foo? redirect; # nginx config

is equivalent to the following Lua code

return ngx.redirect('/foo'); -- Lua code

while

rewrite ^ /foo? permanent; # nginx config

is equivalent to

return ngx.redirect('/foo', ngx.HTTP_MOVED_PERMANENTLY) -- Lua code

URI arguments can be specified as well, for example:

return ngx.redirect('/foo?a=3&b=4')

It is strongly recommended to combine the return statement with this call, i.e., return ngx.redirect(...).

ngx.send_headers

syntax:ngx.send_headers()

context:rewrite_by_lua, access_by_lua, content_by_lua*

Explicitly send out the response headers.

Note that there is normally no need to manually send out response headers as ngx_lua will automatically send headers out
before content is output with ngx.say or ngx.print or when content_by_lua exits normally.

ngx.headers_sent

syntax:value = ngx.headers_sent

context:set_by_lua, rewrite_by_lua, access_by_lua, content_by_lua**

Returns true if the response headers have been sent (by ngx_lua), and false otherwise.

This API was first introduced in ngx_lua v0.3.1rc6.

ngx.print

syntax:ngx.print(...)

context:rewrite_by_lua, access_by_lua, content_by_lua*

Emits arguments concatenated to the HTTP client (as response body). If response headers have not been sent, this function will send headers out first and then output body data.

This is an asynchronous call and will return immediately without waiting for all the data to be written into the system send buffer. To run in synchronous mode, call ngx.flush(true) after calling ngx.print. This can be particularly useful for streaming output. See ngx.flush for more details.

There is a hard coded 2048 byte limitation on error message lengths in the Nginx core. This limit includes trailing newlines and leading time stamps. If the message size exceeds this limit, Nginx will truncate the message text accordingly. This limit can be manually modified by editing the NGX_MAX_ERROR_STR macro definition in the src/core/ngx_log.h file in the Nginx source tree.

ngx.flush

syntax:ngx.flush(wait?)

context:rewrite_by_lua, access_by_lua, content_by_lua*

Flushes response output to the client.

ngx.flush accepts an optional boolean wait argument (Default: false) first introduced in the v0.3.1rc34 release. When called with the default argument, it issues an asynchronous call (Returns immediately without waiting for output data to be written into the system send buffer). Calling the function with the wait argument set to true switches to synchronous mode.

In synchronous mode, the function will not return until all output data has been written into the system send buffer or until the send_timeout setting has expired. Note that using the Lua coroutine mechanism means that this function does not block the Nginx event loop even in the synchronous mode.

When ngx.flush(true) is called immediately after ngx.print or ngx.say, it causes the latter functions to run in synchronous mode. This can be particularly useful for streaming output.

Note that ngx.flush is non functional when in the HTTP 1.0 output buffering mode. See HTTP 1.0 support.

ngx.exit

syntax:ngx.exit(status)

context:rewrite_by_lua, access_by_lua, content_by_lua*

When status >= 200 (i.e., ngx.HTTP_OK and above), it will interrupt the execution of the current request and return status code to nginx.

When status == 0 (i.e., ngx.OK), it will only quit the current phase handler (or the content handler if the content_by_lua directive is used) and continue to run later phases (if any) for the current request.

The status argument can be ngx.OK, ngx.ERROR, ngx.HTTP_NOT_FOUND,
ngx.HTTP_MOVED_TEMPORARILY, or other HTTP status constants.

To return an error page with custom contents, use code snippets like this:

ngx.status = ngx.HTTP_GONE
ngx.say("This is our own content")
-- to cause quit the whole request rather than the current phase handler
ngx.exit(ngx.HTTP_OK)

ngx.decode_args

Decodes a URI encoded query-string into a Lua table. This is the inverse function of ngx.encode_args.

The optional max_args argument can be used to specify the maximum number of arguments parsed from the str argument. By default, a maximum of 100 request arguments are parsed (including those with the same name) and that additional URI arguments are silently discarded to guard against potential denial of service attacks.

This argument can be set to zero to remove the limit and to process all request arguments received:

ngx.now

Returns a floating-point number for the elapsed time in seconds (including milliseconds as the decimal part) from the epoch for the current time stamp from the nginx cached time (no syscall involved unlike Lua's date library).

ngx.re.match

Matches the subject string using the Perl-compatible regular expression regex with the optional options.

Only the first occurrence of the match is returned, or nil if no match is found. In case of fatal errors, like seeing bad UTF-8 sequences in UTF-8 mode, a Lua exception will be raised.

When a match is found, a Lua table captures is returned, where captures[0] holds the whole substring being matched, and captures[1] holds the first parenthesized sub-pattern's capturing, captures[2] the second, and so on.

Specify options to control how the match operation will be performed. The following option characters are supported:

a anchored mode (only match from the beginning)
d enable the DFA mode (or the longest token match semantics).
this requires PCRE 6.0+ or else a Lua exception will be thrown.
first introduced in ngx_lua v0.3.1rc30.
i case insensitive mode (similar to Perl's /i modifier)
j enable PCRE JIT compilation, this requires PCRE 8.21+ which
must be built with the --enable-jit option. for optimum performance,
this option should always be used together with the 'o' option.
first introduced in ngx_lua v0.3.1rc30.
m multi-line mode (similar to Perl's /m modifier)
o compile-once mode (similar to Perl's /o modifier),
to enable the worker-process-level compiled-regex cache
s single-line mode (similar to Perl's /s modifier)
u UTF-8 mode. this requires PCRE to be built with
the --enable-utf8 option or else a Lua exception will be thrown.
x extended mode (similar to Perl's /x modifier)

The o option is useful for performance tuning, because the regex pattern in question will only be compiled once, cached in the worker-process level, and shared among all requests in the current Nginx worker process. The upper limit of the regex cache can be tuned via the lua_regex_cache_max_entries directive.

The optional fourth argument, ctx, can be a Lua table holding an optional pos field. When the pos field in the ctx table argument is specified, ngx.re.match will start matching from that offset. Regardless of the presence of the pos field in the ctx table, ngx.re.match will always set this pos field to the position after the substring matched by the whole pattern in case of a successful match. When match fails, the ctx table will be left intact.

The ctx table argument combined with the a regex modifier can be used to construct a lexer atop ngx.re.match.

Note that, the options argument is not optional when the ctx argument is specified and that the empty Lua string ("") must be used as placeholder for options if no meaningful regex options are required.

To confirm that PCRE JIT is enabled, activate the Nginx debug log by adding the --with-debug option to Nginx or ngx_openresty's ./configure script. Then, enable the "debug" error log level in error_log directive. The following message will be generated if PCRE JIT is enabled:

for m in ngx.re.gmatch("hello, world!", "([a-z]+)", "i")
ngx.say(m[0])
ngx.say(m[1])
end

The optional options argument takes exactly the same semantics as the ngx.re.match method.

The current implementation requires that the iterator returned should only be used in a single request. That is, one should not assign it to a variable belonging to persistent namespace like a Lua package.

ngx.re.sub

Substitutes the first match of the Perl-compatible regular expression regex on the subject argument string with the string or function argument replace. The optional options argument has exactly the same meaning as in ngx.re.match.

This method returns the resulting new string as well as the number of successful substitutions, or throw out a Lua exception when an error occurred (syntax errors in the <replace> string argument, for example).

When the replace is a string, then it is treated as a special template for string replacement. For example,

Do not use backlashes to escape dollar signs; it will not work as expected.

When the replace argument is of type "function", then it will be invoked with the "match table" as the argument to generate the replace string literal for substitution. The "match table" fed into the replace function is exactly the same as the return value of ngx.re.match. Here is an example:

The number 8 will be consistently output when accessing /get regardless of how many Nginx workers there are because the dogs dictionary resides in the shared memory and visible to all of the worker processes.

The shared dictionary will retain its contents through a server config reload (either by sending the HUP signal to the Nginx process or by using the -s reload command-line option).

The contents in the dictionary storage will be lost, however, when the Nginx server quits.

Unconditionally sets a key-value pair into the shm-based dictionary ngx.shared.DICT. Returns three values:

success: boolean value to indicate whether the key-value pair is stored or not.

err: textual error message, can be "no memory".

forcible: a boolean value to indicate whether other valid items have been removed forcibly when out of storage in the shared memory zone.

The value argument inserted can be Lua booleans, numbers, strings, or nil. Their value type will also be stored into the dictionary and the same data type can be retrieved later via the get method.

The optional exptime argument specifies expiration time (in seconds) for the inserted key-value pair. The time resolution is 0.001 seconds. If the exptime takes the value 0 (which is the default), then the item will never be expired.

The optional flags argument specifies a user flags value associated with the entry to be stored. It can also be retrieved later with the value. The user flags is stored as an unsigned 32-bit integer internally. Defaults to 0. The user flags argument was first introduced in the v0.5.0rc2 release.

When it fails to allocate memory for the current key-value item, then set will try removing existing items in the storage according to the Least-Recently Used (LRU) algorithm. Note that, LRU takes priority over expiration time here. If up to tens of existing items have been removed and the storage left is still insufficient (either due to the total capacity limit specified by lua_shared_dict or memory segmentation), then the err return value will be no memory and success will be false.

If this method succeeds in storing the current item by forcibly removing other not-yet-expired items in the dictionary via LRU, the forcible return value will be true. If it stores the item without forcibly removing other valid items, then the return value forcible will be false.

The first argument to this method must be the dictionary object itself, for example,

ngx.shared.DICT.incr

Increments the (numerical) value for key in the shm-based dictionary ngx.shared.DICT by the step value value. Returns the new resulting number if the operation is successfully completed or nil and an error message otherwise.

The key must already exist in the dictionary, otherwise it will return nil and "not found".

If the original value is not a valid Lua number in the dictionary, it will return nil and "not a number".

The value argument can be any valid Lua numbers, like negative numbers or floating-point numbers.

udpsock:setpeername

Attempts to connect a UDP socket object to a remote server or to a datagram unix domain socket file. Because the datagram protocol is actually connection-less, this method does not really establish a "connection", but only just set the name of the remote peer for subsequent read/write operations.

Both IP addresses and domain names can be specified as the host argument. In case of domain names, this method will use Nginx core's dynamic resolver to parse the domain name without blocking and it is required to configure the resolver directive in the nginx.conf file like this:

resolver 8.8.8.8; # use Google's public DNS nameserver

If the nameserver returns multiple IP addresses for the host name, this method will pick up one randomly.

In case of error, the method returns nil followed by a string describing the error. In case of success, the method returns 1.

local sock = ngx.socket.udp()
local ok, err = sock:setpeername("unix:/tmp/some-datagram-service.sock")
if not ok then
ngx.say("failed to connect to the datagram unix domain socket: ", err)
return
end

assuming the datagram service is listening on the unix domain socket file /tmp/some-datagram-service.sock.

Calling this method on an already connected socket object will cause the original connection to be closed first.

This method was first introduced in the v0.5.7 release.

udpsock:send

syntax:ok, err = udpsock:send(data)

context:rewrite_by_lua, access_by_lua, content_by_lua*

Sends data on the current UDP or datagram unix domain socket object.

In case of success, it returns 1. Otherwise, it returns nil and a string describing the error.

The input argument data can either be a Lua string or a (nested) Lua table holding string fragments. In case of table arguments, this method will automatically copy all the string elements piece by piece to the underlying Nginx socket send buffers, which is usually optimal than doing string concatenation operations on the Lua land.

In case of success, it returns the data received; in case of error, it returns nil with a string describing the error.

If the size argument is specified, then this method will use this size as the receive buffer size. But when this size is greater than 8192, then 8192 will be used instead.

If no argument is specified, then the maximal buffer size, 8192 is assumed.

Timeout for the reading operation is controlled by the lua_socket_read_timeout config directive and the settimeout method. And the latter takes priority. For example:

sock:settimeout(1000) -- one second timeout
local data, err = sock:receive()
if not data then
ngx.say("failed to read a packet: ", data)
return
end
ngx.say("successfully read a packet: ", data)

It is important here to call the settimeout method before calling this method.

This feature was first introduced in the v0.5.7 release.

udpsock:close

syntax:ok, err = udpsock:close()

context:rewrite_by_lua, access_by_lua, content_by_lua*

Closes the current UDP or datagram unix domain socket. It returns the 1 in case of success and returns nil with a string describing the error otherwise.

For socket objects that have not invoked this method, they (and their connections) will be automatically closed when the socket object is released by the Lua GC (Garbage Collector) or the current client HTTP request finishes processing.

This feature was first introduced in the v0.5.7 release.

udpsock:settimeout

syntax:udpsock:settimeout(time)

context:rewrite_by_lua, access_by_lua, content_by_lua*

Set the timeout value in milliseconds for subsequent socket operations (like receive).

tcpsock:connect

Attempts to connect a TCP socket object to a remote server or to a stream unix domain socket file without blocking.

Before actually resolving the host name and connecting to the remote backend, this method will always look up the connection pool for matched idle connections created by previous calls of this method (or the ngx.socket.connect function).

Both IP addresses and domain names can be specified as the host argument. In case of domain names, this method will use Nginx core's dynamic resolver to parse the domain name without blocking and it is required to configure the resolver directive in the nginx.conf file like this:

resolver 8.8.8.8; # use Google's public DNS nameserver

If the nameserver returns multiple IP addresses for the host name, this method will pick up one randomly.

In case of error, the method returns nil followed by a string describing the error. In case of success, the method returns 1.

It is important here to call the settimeout method before calling this method.

Calling this method on an already connected socket object will cause the original connection to be closed first.

An optional Lua table can be specified as the last argument to this method to specify various connect options:

pool
specify a custom name for the connection pool being used. If omitted, then the connection pool name will be automatically generated from the string template "<host>:<port>" or "<unix-socket-path>".

The support for the options table argument was first introduced in the v0.5.7 release.

This method was first introduced in the v0.5.0rc1 release.

tcpsock:send

syntax:bytes, err = tcpsock:send(data)

context:rewrite_by_lua, access_by_lua, content_by_lua*

Sends data without blocking on the current TCP or Unix Domain Socket connection.

This method is a synchronous operation that will not return until all the data has been flushed into the system socket send buffer or an error occurs.

In case of success, it returns the total number of bytes that have been sent. Otherwise, it returns nil and a string describing the error.

The input argument data can either be a Lua string or a (nested) Lua table holding string fragments. In case of table arguments, this method will automatically copy all the string elements piece by piece to the underlying Nginx socket send buffers, which is usually optimal than doing string concatenation operations on the Lua land.

Timeout for the sending operation is controlled by the lua_socket_send_timeout config directive and the settimeout method. And the latter takes priority. For example:

sock:settimeout(1000) -- one second timeout
local bytes, err = sock:send(request)

It is important here to call the settimeout method before calling this method.

This feature was first introduced in the v0.5.0rc1 release.

tcpsock:receive

syntax:data, err, partial = tcpsock:receive(size)

syntax:data, err, partial = tcpsock:receive(pattern?)

context:rewrite_by_lua, access_by_lua, content_by_lua*

Receives data from the connected socket according to the reading pattern or size.

This method is a synchronous operation just like the send method and is 100% nonblocking.

In case of success, it returns the data received; in case of error, it returns nil with a string describing the error and the partial data received so far.

If a number-like argument is specified (including strings that look like numbers), then it is interpreted as a size. This method will not return until it reads exactly this size of data or an error occurs.

If a non-number-like string argument is specified, then it is interpreted as a "pattern". The following patterns are supported:

'*a': reads from the socket until the connection is closed. No end-of-line translation is performed;

'*l': reads a line of text from the socket. The line is terminated by a Line Feed (LF) character (ASCII 10), optionally preceded by a Carriage Return (CR) character (ASCII 13). The CR and LF characters are not included in the returned line. In fact, all CR characters are ignored by the pattern.

If no argument is specified, then it is assumed to be the pattern '*l', that is, the line reading pattern.

Timeout for the reading operation is controlled by the lua_socket_read_timeout config directive and the settimeout method. And the latter takes priority. For example:

sock:settimeout(1000) -- one second timeout
local line, err, partial = sock:receive()
if not line then
ngx.say("failed to read a line: ", err)
return
end
ngx.say("successfully read a line: ", line)

It is important here to call the settimeout method before calling this method.

This feature was first introduced in the v0.5.0rc1 release.

tcpsock:receiveuntil

syntax:iterator = tcpsock:receiveuntil(pattern, options?)

context:rewrite_by_lua, access_by_lua, content_by_lua*

This method returns an iterator Lua function that can be called to read the data stream until it sees the specified pattern or an error occurs.

Here is an example for using this method to read a data stream with the boundary sequence --abcedhb:

local reader = sock:receiveuntil("\r\n--abcedhb")
local data, err, partial = reader()
if not data then
ngx.say("failed to read the data stream: ", err)
end
ngx.say("read the data stream: ", data)

When called without any argument, the iterator function returns the received data right before the specified pattern string in the incoming data stream. So for the example above, if the incoming data stream is 'hello, world! -agentzh\r\n--abcedhb blah blah', then the string 'hello, world! -agentzh' will be returned.

In case of error, the iterator function will return nil along with a string describing the error and the partial data bytes that have been read so far.

The iterator function can be called multiple times and can be mixed safely with other cosocket method calls or other iterator function calls.

The iterator function behaves differently (i.e., like a real iterator) when it is called with a size argument. That is, it will read that size of data on each invocation and will return nil at the last invocation (either sees the boundary pattern or meets an error). For the last successful invocation of the iterator function, the err return value will be nil too. The iterator function will automatically reset after its last successful invocation that returns nil data and nil error. Consider the following example:

local reader = sock:receiveuntil("\r\n--abcedhb")
while true then
local data, err, partial = reader(4)
if not data then
if err then
ngx.say("failed to read the data stream: ", err)
break
end
ngx.say("read done")
break
end
ngx.say("read chunk: [", data, "]")
end

Then for the incoming data stream 'hello, world! -agentzh\r\n--abcedhb blah blah', we shall get the following output from the sample code above:

Note that, the actual data returned might be a little longer than the size limit specified by the size argument when the boundary pattern has ambiguity for streaming parsing. Near the boundary of the data stream, the data string actually returned could also be shorter than the size limit.

Timeout for the iterator function's reading operation is controlled by the lua_socket_read_timeout config directive and the settimeout method. And the latter takes priority. For example:

local readline = sock:receiveuntil("\r\n")
sock:settimeout(1000) -- one second timeout
line, err, partial = readline()
if not line then
ngx.say("failed to read a line: ", err)
return
end
ngx.say("successfully read a line: ", line)

It is important here to call the settimeout method before calling the iterator function (note that the receiveuntil call is irrelevant here).

As from the v0.5.1 release, this method also takes an optional options table argument to control the behavior. The following options are supported:

inclusive

The inclusive takes a boolean value to control whether to include the pattern string in the returned data string. Default to false. For example,

Then for the input data stream "hello world _END_ blah blah blah", then the example above will output hello world _END_, including the pattern string _END_ itself.

This method was first introduced in the v0.5.0rc1 release.

tcpsock:close

syntax:ok, err = tcpsock:close()

context:rewrite_by_lua, access_by_lua, content_by_lua*

Closes the current TCP or stream unix domain socket. It returns the 1 in case of success and returns nil with a string describing the error otherwise.

For socket objects that have invoked the setkeepalive method, there is no need to call this method on it because the socket object is already closed (and the current connection is saved into the built-in connection pool).

For socket objects that have not invoked setkeepalive nor this method, they (and their connections) will be automatically closed when the socket object is released by the Lua GC (Garbage Collector) or the current client HTTP request finishes processing.

This feature was first introduced in the v0.5.0rc1 release.

tcpsock:settimeout

syntax:tcpsock:settimeout(time)

context:rewrite_by_lua, access_by_lua, content_by_lua*

Set the timeout value in milliseconds for subsequent socket operations (connect, receive, and iterators returned from receiveuntil).

tcpsock:setoption

This function is added for LuaSocket API compatibility and does nothing for now. Its functionality will be implemented in future.

This feature was first introduced in the v0.5.0rc1 release.

tcpsock:setkeepalive

syntax:ok, err = tcpsock:setkeepalive(timeout?, size?)

context:rewrite_by_lua, access_by_lua, content_by_lua*

Puts the current socket's connection into the cosocket built-in connection pool and keep it alive until other connect method calls request it or the associated maximal idle timeout is expired.

The first optional argument, timeout, can be used to specify the maximal idle timeout (in milliseconds) for the current connection. If omitted, the default setting in the lua_socket_keepalive_timeout config directive will be used. If the 0 value is given, then the timeout interval is unlimited.

The second optional argument, size, can be used to specify the maximal number of connections allowed in the connection pool for the current server (i.e., the current host-port pair or the unix domain socket file path). Note that the size of the connection pool cannot be changed once the pool is created. When this argument is omitted, the default setting in the lua_socket_pool_size config directive will be used.

When the connection pool is exceeding the size limit, the least recently used (idle) connection already in the pool will be closed automatically to make room for the current connection.

Note that the cosocket connection pool is per Nginx worker process rather than per Nginx server instance, so the size limit specified here also applies to every single Nginx worker process.

Idle connections in the pool will be monitored for any exceptional events like connection abortion or unexpected incoming data on the line, in which cases the connection in question will be closed and removed from the pool.

In case of success, this method returns 1; otherwise, it returns nil and a string describing the error.

This method also makes the current cosocket object enter the "closed" state, so there is no need to manually call the close method on it afterwards.

This feature was first introduced in the v0.5.0rc1 release.

tcpsock:getreusedtimes

syntax:count, err = tcpsock:getreusedtimes()

context:rewrite_by_lua, access_by_lua, content_by_lua*

This method returns the (successfully) reused times for the current connection. In case of error, it returns nil and a string describing the error.

If the current connection does not come from the built-in connection pool, then this method always returns 0, that is, the connection has never been reused (yet). If the connection comes from the connection pool, then the return value is always non-zero. So this method can also be used to determine if the current connection comes from the pool.

Lua/LuaJIT bytecode support

As from the v0.5.0rc32 release, all *_by_lua_file configure directives (such as content_by_lua_file) support loading Lua 5.1 and LuaJIT 2.0 raw bytecode files directly.

Please note that the bytecode format used by LuaJIT 2.0 is not compatible with that for the standard Lua 5.1 interpreter. So if using LuaJIT 2.0 with ngx_lua, LuaJIT-compatible bytecode files must be generated as shown:

Loading bytecode files via the Lua primitives like require and dofile should always work as expected.

HTTP 1.0 support

The HTTP 1.0 protocol does not support chunked outputs and always requires an
explicit Content-Length header when the response body is non-empty in order to support the HTTP 1.0 keep-alive (as required by the ApacheBench (ab) tool). So when
an HTTP 1.0 request is present and the lua_http10_buffering directive is turned on, this module will automatically buffer all the
outputs of user calls of ngx.say and ngx.print and
postpone sending response headers until it sees all the outputs in the response
body, and at that time ngx_lua can calculate the total length of the body and
construct a proper Content-Length header for the HTTP 1.0 client.

If the user Lua code sets the Content-Length response header itself, then the automatic buffering will be disabled even if the lua_http10_buffering directive is turned on.

For large streaming output responses, it is important to disable the lua_http10_buffering directive to minimise memory usage.

Data Sharing within an Nginx Worker

NOTE: This mechanism behaves differently when code cache is turned off and should be considered a DIRTY TRICK. Note that backward compatibility is NOT guaranteed and that there may be other undesirable consequences. A new data sharing mechanism will be designed later.

To globally share data among all the requests handled by the same nginx worker process, encapsulate the shared data into a Lua module, use the Lua require builtin to import the module, and then manipulate the shared data in Lua. This works because required Lua modules are loaded only once and all coroutines will share the same copy of the module. Note however that Lua global variables WILL NOT persist between requests because of the one-coroutine-per-request isolation design.

The mydata module in this example will only be loaded and run on the first request to the location /lua,
and all subsequent requests to the same nginx worker process will use the reloaded instance of the
module as well as the same copy of the data in it, until a HUP signal is sent to the Nginx master process to force a reload.
This data sharing technique is essential for high performance Lua applications based on this module.

Note that this data sharing is on a per-worker basis and not on a ''per-server' basis'. That is, when there are multiple nginx worker processes under an Nginx master, data sharing cannot cross the process boundary between these workers.

If server wide data sharing is required:
1. Use the ngx.shared.DICT API provided by this module.
1. Use only a single nginx worker and a single server. This is however not recommended when there is a multi core CPU or multiple CPUs in a single machine.
1. Use data storage mechanisms such as memcached, redis, MySQL or PostgreSQL. The ngx_openresty bundle associated with this module comes with a set of companion Nginx modules that provide interfaces with these data storage mechanisms. See the HttpMemcModule, HttpRedis2Module, HttpDrizzleModule and HttpPostgresModule modules for details

Known Issues

TCP socket connect operation issues

The tcpsock:connect method may indicate success despite connection failures such as with Connection Refused errors.

However, later attempts to manipulate the cosocket object will fail and return the actual error status message generated by the failed connect operation.

This issue is due to limitations in the Nginx event model and only appears to affect Mac OS X.

Lua Coroutine Yielding/Resuming

As the module's predefined Nginx I/O API uses the coroutine yielding/resuming mechanism, user code should not call any Lua modules that use the Lua coroutine mechanism in order to prevent conflicts with the module's predefined Nginx API methods such as ngx.location.capture (Actually, coroutine modules have been masked off in content_by_lua directives and others). This limitation is significant and work is ongoing on an alternative coroutine implementation that can fit into the Nginx event model to address this. When this is done, it will be possible to use the Lua coroutine mechanism freely as it is in standard Lua implementations.

Lua's dofile builtin is implemented as a C function in both Lua 5.1 and LuaJIT 2.0 and when ngx.location.capture is called, ngx.exec, ngx.exit or ngx.req.read_body or similar in the file to be loaded by dofile, a coroutine yield across the C function boundary will be initiated. This however is not normally allowed within ngx_lua and will usually result in error messages like lua handler aborted: runtime error: attempt to yield across C-call boundary. To avoid this, define a real Lua module and use the Lua require builtin instead.

Lua Variable Scope

Care should be taken when importing modules and this form should be used:

local xxx = require('xxx')
instead of the old deprecated form:
require('xxx')
If the old form is required, force reload the module for every request by using the `package.loaded.<module>` command:
package.loaded.xxx = nil
require('xxx')

It is recommended to always place the following piece of code at the end of Lua modules that use the ngx.location.capture or ngx.location.capture_multi directives to prevent casual use of module-level global variables that are shared among all requests:

Assuming the current Lua module is named foo.bar, this will guarantee that local variables in module foo.bar functions have been declared as "local". It prevents undesirable race conditions while accessing such variables. See Data Sharing within an Nginx Worker for the reasons behind this.

Special PCRE Sequences

PCRE sequences such as \d, \s, or \w, require special attention because in string literals, the backslash character, \, is stripped out by both the Lua language parser and by the Nginx config file parser before processing. So the following snippet will not work as expected:

Here, \\\\d+ is stripped down to \\d+ by the Nginx config file parser and this is further stripped down to \d+ by the Lua language parser before running.

Alternatively, the regex pattern can be presented as a long-bracketed Lua string literal by encasing it in "long brackets", [[...]], in which case backslashes have to only be escaped once for the Nginx config file parser.

An alternative approach to escaping PCRE sequences is to ensure that Lua code is placed in external script files and executed using the various *_by_lua_file directives.
With this approach, the backslashes are only stripped by the Lua language parser and therefore only need to be escaped once each.

coding up arbitrarily complex web applications in a content handler using synchronous but still non-blocking access to the database backends and other storage,

doing very complex URL dispatch in Lua at rewrite phase,

using Lua to implement advanced caching mechanism for Nginx's subrequests and arbitrary locations.

The possibilities are unlimited as the module allows bringing together various elements within Nginx as well as exposing the power of the Lua language to the user. The module provides the full flexibility of scripting while offering performance levels comparable with native C language programs both in terms of CPU time as well as memory footprint. This is particularly the case when LuaJIT 2.0 is enabled.

Code Repository

Installation

The ngx_openresty bundle can be used to install Nginx, ngx_lua, either one of the standard Lua 5.1 interpreter or LuaJIT 2.0, as well as a package of powerful companion Nginx modules. The basic installation step is a simple ./configure --with-luajit && make && make install.

Alternatively, ngx_lua can be manually compiled into Nginx:

Install LuaJIT 2.0 (Recommended) or Lua 5.1 (Lua 5.2 is not supported yet). LuajIT can be downloaded from the the LuaJIT project website and Lua 5.1, from the Lua project website. Some distribution package managers also distribute LuajIT and/or Lua.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.